Influence of the negative charge density of metalate nanosheets on their bottom-up synthesis

Abstract

The influence of the negative charge densities of metalate nanosheets on their bottom-up syntheses was examined. Metalate nanosheets are usually prepared by exfoliating layered metalates. For each metalate, the bottom-up synthesis yields only one type of nanosheet structure, although different layered structures are known. In this work, we compared the crystal structures of different layered metalates, and the results indicate that metalate nanosheets with the lowest negative charge density were formed for each metalate. Next, we examined the effect of the oxidation state of metal ions on the bottom-up synthesis of metalate nanosheets, because the negative charge density of the metalate sheets can be modified according to the oxidation state of the metal ion. For the bottom-up synthesis of manganate nanosheets, the lowest Mn oxidation state, which can be between 3 and 4, was as large as 3.65. Thus, their negative charge densities were relatively small. Additionally, cobaltate nanosheets could not be obtained via the bottom-up process; however, the oxidation of layered cobaltates led to the intercalation of bulky cations and water into the interlayer. These results suggest that low negative charge density is required for the bottom-up synthesis of metalate nanosheets.